Article Posted on : - Dec 10, 2008

An artis's impression of the Jupiter-size extrasolar planet, HD 189733b, being eclipsed by its parent star. NASA photo

WASHINGTON (BNS): NASA's Hubble Space Telescope has achieved a major breakthrough by discovering carbon dioxide in the atmosphere of a planet orbiting another star. This is a first step in finding chemical bio-tracers of extra-terrestrial life.

Hubble’s observation of Jupiter-sized planet HD 189733b is a proof that basic chemistry for life can be measured on planets orbiting other stars, according to NASA scientists.

"Organic compounds also can be a by-product of life processes and their detection on an Earth-like planet someday may provide the first evidence of life beyond the planet," NASA said.

During earlier observations of HD 189733b, Hubble and Spitzer Space Telescope found water vapour, while early this year, Hubble found methane in the planet's atmosphere.

Eric Smith, Hubble Space Telescope programme scientist at NASA Headquarters said, “Hubble was conceived primarily for observations of the distant universe, yet it was opening a new era of astrophysics and comparative planetary science”.

"These atmospheric studies will begin to determine the compositions and chemical processes operating on distant worlds orbiting other stars. The future for this newly opened frontier of science is extremely promising as we expect to discover many more molecules in exoplanet atmospheres”.

Mark Swain, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, said that gases in the planet's atmosphere absorb certain wavelengths of light from the planet's hot glowing interior. He made the observation while using the Hubble's near infrared camera and multi-object spectrometer to study infrared light emitted from the planet, which lies 63 light-years away.

The California scientist, through the study, identified carbon dioxide and carbon monoxide. "The molecules leave a unique spectral fingerprint on the radiation from the planet that reaches Earth. This is the first time a near-infrared emission spectrum has been obtained for an exoplanet," he said.

"The carbon dioxide is the main reason for the excitement because, under the right circumstances, it could have a connection to biological activity as it does on Earth. The very fact we are able to detect it and estimate its abundance is significant for the long-term effort of characterising planets to find out what they are made of and if they could be a possible host for life," Swain said.

Explaining in depth about the observation, he said the best time would be on planets with orbits tilted edge-on to Earth. "They routinely pass in front of and then behind their parent stars, a phenomena known as eclipses. The planet HD 189733b passes behind its companion star once every 2.2 days. The eclipses allow an opportunity to subtract the light of the star alone when the planet is blocked from that of the star and planet together prior to eclipse. That isolates the emission of the planet and makes possible a chemical analysis of its atmosphere."

Another team member Guatam Vasisht of NASA's Jet Propulsion Laboratory said in this way, one is using the eclipse of the planet behind the star to probe the planet's day side, which contains the hottest portions of its atmosphere. "We are starting to find the molecules and to figure out how many there are to see the changes between the day side and the night side."

California scientist Swain said after the launch of NASA's James Webb Space Telescope in 2013, astronomers would be able to look at the near-infrared light emitted from a planet. "These biomarkers are best seen at near-infrared wavelengths. And astronomers can look forward to using the James Webb Space Telescope to look spectroscopically for biomarkers on a terrestrial planet the size of Earth or a "super-Earth" several times our planet's mass," he said, adding, the Webb telescope should be able to make much more sensitive measurements of these primary and secondary eclipse events.